As an IP-based network architecture proposed by the 3rd Generation Partnership Project (3GPP), an IMS network constructs an open and flexible service environment, supports multimedia applications, and provides rich multimedia services for user terminals. The IMS is an IP-based telecommunication network architecture, which is independent of access technologies, and can provide services not only for packet access networks such as General Packet Radio Service (GPRS), Wireless Local Area Network (WLAN) and the like, but also for mobile cellular networks such as Global System for Mobile communications (GSM), Universal Mobile Telecommunications System (UMTS) and the like.
In the IMS, status presence is a service that notifies one user terminal of accessibility, availability and communication desire of another user terminal. The status presence service can show whether other user terminals are online, or, show status information of these user terminals when they are online, that is, show whether the user terminals are idle or busy (for example, they are in conference, on the phone or the like). Besides, the status presence service can enable the user terminals to provide detailed information of communication modes and communication capabilities, for example, the status can present whether the user terminals have such capabilities as audio, video, instant message and the like. The implementation of this service is generally realized through release, subscription and notification of status presence information.
In a typical IMS network, based on features of the presence service, the realization of the presence service among user terminals puts forward higher requirements on transmission capacity of a great deal of information, high frequency, and strong burst processing capability of the whole network device in the IMS network than realization of other services. In order to guarantee smooth presence service, the processing capability of each relevant device has to be improved on one hand, and the processing flow of the service has to be simplified on software on the other hand.
FIG. 1 shows a schematic diagram of a reference frame of an IMS presence service, as shown in FIG. 1, an IMS terminal plays two roles of an observer and a Presence User Agent (PUA); a Presence Agent (PA) is an Application Server (AS) located in a home network. A Resource List Server (RLS) is also suitable for realizing functions of an application server, and an AS providing other services can serve as the observer of a Presence Entity (PE). Most of interfaces interacted among devices realize the function of status presence of Session Initialization Protocol (SIP) interfaces or Diameter interfaces of an IMS. For a Pen interface, it allows an application server to act as a PUA to release status presence information to a PA of a PE. The PUA can obtain status information of a user terminal from any possible information sources, such as Home Location Register (HLR) in the a circuit switching network, Service GPRS Support Node (SGSN) in a GPRS network, or Service-Call Session Control Function (S-CSCF) registered by the IMS.
FIG. 2 shows a flow chart of an IMS terminal subscribing a status information list in an RLS, as shown in FIG. 2, the flow of realizing status presence in an IMS network comprises the following steps:
step 201: an observer application program in the IMS terminal sends a Subscribe request to the status presence list of the observer application program, the Event header field of the request is set as Eventilist to indicate that the request is sent to a list rather than a single PE;
step 202-step 203: the Subscribe request is forwarded to an Interrogating-Call Session Control Function (I-CSCF) via a Session Border Controller (SBC) and then forwarded to an S-CSCF, at this moment, an initial filtering rule is triggered;
step 204: the filtered rule is forwarded to a related application server functioned as the RLS;
step 205-step 208: after verifying the identity of the requestor and authorizing the subscription, the RLS sends a response 200OK and forwards it to the IMS terminal via the S-CSCF, a P-CSCF and the SBC;
step 209-step 212: the RLS sends a NOTIFY request, although the NOTIFY request contains no status presence information and needs to be forwarded to the IMS terminal via the S-CSCF and the P-CSCF;
step 213-step 216: the IMS terminal responds with 200OK and forwards it to the RLS via the S-CSCF, the P-CSCF and the SBC; and
step 217-step 220: the RLS subscribes information of all PEs one by one jn a resource list; when collecting enough information, the RLS generates another NOTIFY request and forwards it to the IMS terminal via the S-CSCF, the P-CSCF and the SBC. The NOTIFY request contains all presence information received from the PUAs of the PEs.
It can be seen from the flow chart shown in FIG. 2 that, whenever one IMS terminal observer wants to subscribe status presence information of a PE, the IMS terminal observer needs to adopt a Subscribe command and a NOTIFY command to interact with the RLS; even in the case of least interaction, both the IMS terminal observer and the RLS need to perform interaction using SIP commands for six times.
FIG. 3 shows a flow chart that the RLS subscribes information of one PE in the resource list, as shown in FIG. 3, the specific steps are as follows:
step 301-step 306: the RLS sends a Subscribe request, whose Event header field is set as Presence, to one PE in the resource list, an S-CSCF in an RLS home network forwards the Subscribe request to an I-CSCF in a network where the PE is located, and the I-CSCF searches HSS through a Diameter interface to obtain the S-CSCF where the PE is located, and forwards the Subscribe request to a PA;
step 307-step 310: the PA responds with 200OK and forwards it to the RLS via the I-CSCF;
step 311: the PA sends a NOTIFY message containing status presence information of the PE, and directly forwards it to the S-CSCF in the RLS network;
step 312: the S-CSCF in the RLS network forwards the NOTIFY message coming from the PA to the RLS; and
step 313-step 314: the RLS responds with 200OK and forwards it to the PA via the S-CSCF.
It can be seen from the processing flows shown in FIG. 2 and FIG. 3 that, if one IMS terminal wants to realize a subscription to one PE, in the visited network and home network of the initiator, the IMS terminal and the RLS need to perform interaction with at least six SIP signalings, devices between the IMS terminal and the RLS also need to process at least twelve signalings. The RLS in a core network also needs four signalings to perform interaction. The presence service allows one user terminal to subscribe information of multiple PEs and allows multiple user terminals to subscribe crisscross, thus the PEs change frequently, this may cause NOTIFY information explosion and highly frequent generation of a great deal of information. Therefore, the application servers and the network devices in the IMS will be impacted significantly and normal allocation of call resources and occupation of capacity resources will be influenced.